We start off with a bird in the nest box. I'm not sure whether it's male or female.
Here's an interesting maneuver at Box1
It appears to be leaving the box, but doesn't leave go of it ...
S ... but swivels round ...
... and has a look around instead.
In Box2, we have another visitor. He looks male judging by the condition of his head feathers.
Yes - definitely male.
Just to prove I'm right, the female follows him inside the box.
Of course, he immediately starts to leave.
Away he goes!